The type of the invention referred to is well known in the art which generally comprises a container, a mouthpiece engageable with the container and a cap served for covering the mouthpiece. Nevertheless, the volume of the feeding bottle is constant so that it is often necessary to prepare a small-sized feeding bottle in addition to the normal-sized feeding bottle. The small-sized feeding bottle is used for feeding liquids such as juice, or the like to the infant while the normal-sized feeding bottle is used for feeding milk or the like to the infant. Accordingly, it is necessary to prepare at least two feeding bottles for an infant. Furthermore, it will cause much inconvenience when carrying the infant outside.